The antecedent of “they” is not clear. Even though logically “they” should refer to “scientists”, structurally “they” seems to modify “life-forms”, producing an illogical meaning that these life-forms emerged earlier than these life forms had previously thought!!

Option Analysis

(A) Incorrect. For the errors described above.

(B) Incorrect. For the following reasons:

Error no. 1 of the original sentence

The use of past perfect “had been” is incorrect. There is no action in the simple past with which this action “previously thought” needs to be sequenced.

(C) Correct. All the errors in the original sentence have been rectified. Please observe that the structure “earlier than previously thought” is correct.

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